Apparatus for and method of controlling engine

ABSTRACT

The present invention is related to an apparatus for and a method of controlling an engine provided with: a variable operation angle mechanism that is provided for varying a valve operation angle of an engine valve driven by a camshaft, and is capable of varying a center phase of the valve operation angle in response to a variation in the valve operation angle; and a variable valve timing mechanism provided for varying a rotating phase of the camshaft relative to a crankshaft of the engine, in which a target valve operation angle and a target rotating phase is calculated based on the engine operating state, and a correction value for correcting the target rotating phase based on the target valve operation angle is set. Then, the target rotating phase is corrected by the correction value, thereby controlling the variable valve timing mechanism based on the corrected target rotating phase.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for and a method ofcontrolling an engine provided with: a variable operation anglemechanism which varies a valve operation angle of an engine valve drivenby a camshaft and varies a center phase of the valve operation angle inresponse to a variation in the valve operation angle; and a variablevalve timing mechanism which varies a rotating phase of the camshaftrelative to a crankshaft.

2. Description of the Related Art

Japanese Laid-open (Kokai) Patent Application Publication No.2005-291014 discloses a variable operation angle mechanism suitable foruse in an engine to decrease a valve lift amount and to vary a centerphase of a valve operation angle in an advance direction in response toa decrease in the valve operation angle of an intake valve.

Incidentally, in the case where there is employed the combination of thevariable operation angle mechanism which varies the center phase of thevalve operation angle in response to the variation in the valveoperation angle and a variable valve timing mechanism which varies arotating phase of a camshaft relative to a crankshaft of an engine, evenif the rotating phase at that time controlled by the variable valvetiming mechanism is kept at an identical condition, the center phase ofthe valve operation angle might varies depending on the valve operationangle at that time.

Thus, even if the variable valve timing mechanism is controlled based ona desired center phase of the valve operation angle that is demandeddepending on an engine operating state, an actual center phase might beshifted from the target center phase depending on how extent the valveoperation angle is taking at that time.

SUMMARY OF THE INVENTION

In view of the above problems, an object of the present invention is toprovide a novel technique for enabling a center phase of a valveoperation angle of an engine valve to be controlled with high accuracy,in an engine provided with: a variable operation angle mechanism whichvaries the valve operation angle of the engine valve driven by acamshaft and varies the center phase of the valve operation angle inresponse to a variation in the valve operation angle; and a variablevalve timing mechanism which varies a rotating phase of the camshaftrelative to the crankshaft of the engine.

In order to achieve the above object, the present invention providessuch a novel technical concept of calculating a target valve operationangle and a target rotating phase based on a current engine operatingstate taken by an engine, to control the variable operation anglemechanism based on the calculated target valve operation angle, and tocorrect the target rotating phase also based on the calculated targetvalve operation angle, thereby controlling the variable valve timingmechanism based on the corrected target rotating phase.

The other objects and features of this invention will be understood fromthe ensuing description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a systematic construction of anengine according to an embodiment of the present invention;

FIG. 2 is a cross sectional view illustrating a variable operation anglemechanism according to the embodiment of the present invention:

FIG. 3 is a side view illustrating the variable operation anglemechanism according to the embodiment of the present invention:

FIG. 4 is an exploded perspective view illustrating the variableoperation angle mechanism according to the embodiment of the presentinvention;

FIG. 5 is a cross sectional view illustrating the variable operationangle mechanism according to the embodiment of the present invention,staying at its state of low lift;

FIG. 6 is a cross sectional view illustrating the same variableoperation angle mechanism, staying at its state of high lift;

FIG. 7 is a graphical view illustrating variation characteristics of avalve operation angle and a valve lift amount of the variable operationangle mechanism according to the embodiment of the present invention;

FIG. 8 is a cross sectional view illustrating a variable operation anglemechanism according to the embodiment of the present invention, whichmechanism differs from that illustrated in FIGS. 2 through 6 invariation characteristics of the valve operation angle and the valvelift amount;

FIG. 9 is a graphical view illustrating variation characteristics of thevalve operation angle and the valve lift amount of the variableoperation angle mechanism illustrated in FIG. 8;

FIG. 10 is a cross sectional view illustrating a variable valve timingmechanism according to an embodiment of the present invention;

FIG. 11 is a flowchart illustrating a correction control of a targetvalue of the variable valve timing mechanism according to the embodimentof the present invention;

FIG. 12 is a graphical view illustrating a correlation between anaccelerator opening degree ACC, an engine rotating speed NE, and atarget torque according to the embodiment of the present invention;

FIG. 13 is a graphical view illustrating a correlation between thetarget torque, the engine rotating speed NE, and a target value of thevariable operation angle mechanism according to the embodiment of thepresent invention;

FIG. 14 is a graphical view illustrating a correlation between thetarget torque, the engine rotating speed NE, and the target value of thevariable valve timing mechanism according to the embodiment of thepresent invention;

FIG. 15 is a graphical view illustrating a correlation between thetarget value of the variable operation angle mechanism and a correctionvalue for correcting the target value of the variable valve timingmechanism according to the embodiment of the present invention;

FIG. 16 is a flowchart illustrating the correction control of the targetvalue of the variable valve timing mechanism according to the embodimentof the present invention;

FIG. 17 is a diagrammatic view for explaining a control for shiftingopen characteristics of an intake valve from a default state to a targetat an intermediate-load operation according to the embodiment of thepresent invention;

FIG. 18 is a diagrammatic view for explaining a control for shifting theopen characteristics of the intake valve from the target at theintermediate-load operation to a target at a full throttle operationaccording to the embodiment of the present invention;

FIG. 19 is a flowchart illustrating the correction control of the targetvalue, and a failsafe control, of the variable valve timing mechanismaccording to the embodiment of the present invention;

FIG. 20 is a graphical view illustrating variation characteristics ofthe valve operation angle and the valve lift amount of the intake valveaccording to the embodiment of the present invention;

FIG. 21 is a diagrammatic view for indicating a variation in an openingtiming of the intake valve in the case where the intermediate-loadoperation is shifted to the full throttle operation according to theembodiment of the present invention;

FIG. 22 is a time chart illustrating a variation in opening timing IVOof the intake valve caused by the shift from the intermediate-loadoperation to the full throttle operation, when a ratio RIVO, which is aratio of a change amount of opening timing IVO to a change amount of thevalve operation angle, is ret to 50%, according to the embodiment of thepresent invention;

FIG. 23 is a time chart illustrating the variation in the opening timingof the intake valve caused by the shift from the intermediate-loadoperation to the full throttle operation, when ratio RIVO is set to be30%, according to the embodiment of the present invention;

FIG. 24 is a graphical view illustrating a correlation between ratioRIVO and a response time of an intake air amount according to theembodiment of the present invention;

FIG. 25 is a time chart illustrating the variation in the opening timingof the intake valve caused by the shift from an acceleration operationto a constant-speed operation, when ratio RIVO is set to be 50%,according to the embodiment of the present invention;

FIG. 26 a time chart illustrating a variation in the opening timing ofthe intake valve caused by the shift from the acceleration operation tothe constant-speed operation, when ratio RIVO is set to be 30%;

FIG. 27 is a graphical view illustrating a correlation between ratioRIVO and a fuel saving benefit according to the embodiment of thepresent invention;

FIG. 28 is a diagrammatic view for indicating the variation in theopening timing of the intake valve in the case where theintermediate-load operation is shifted to an idle operation according tothe embodiment of the present invention;

FIG. 29 is a time chart illustrating the variation in the opening timingof the intake valve caused by the shift from the intermediate-loadoperation to the idle operation, when ratio RIVO is set to be 50%,according to the embodiment of the present invention;

FIG. 30 is a time chart illustrating the variation in the opening timingof the intake valve caused by the shift from the intermediate-loadoperation to the idle operation, when a ratio RIVO is set to be 0%,according to the embodiment of the present invention; and

FIG. 31 is a graphical view illustrating a correlation between ratioRIVO and the response time of opening timing IVO according to theembodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a block diagram illustrating a systematic construction of avehicular engine according to the present invention.

Referring to FIG. 1, in an intake pipe 102 of an engine (e.g., aninternal combustion engine) 101, there is interposed an electronicallycontrolled throttle 104 in which a throttle motor 103 a varies anopening degree of a throttle valve 103 b.

Via electronically controlled throttle 104 and an intake valve 105,suction of the air takes place into a combustion chamber 106.

In an intake port 130 on an upstream side of intake valve 105, a fuelinjection valve 131 is provided.

Fuel injection valve 131 injects a fuel of an amount proportional to aninjection pulse width of an injection pulse signal provided from an ECM(engine control module) 114.

Then, the fuel in combustion chamber 106 is ignited and combusted by aspark ignition by a not-shown spark plug.

The engine may be an in-cylinder direct injection type engine in whichfuel injection valve 131 directly injects fuel into combustion chamber106, and alternatively the engine may be a compression self-ignitiontype engine instead of the spark ignition type engine.

Combustion exhaust gas in combustion chamber 106 is discharged via anexhaust valve 107 and is purified in a front catalytic converter 108 anda rear catalytic converter 109, and is then discharged into theatmosphere.

Exhaust valve 107 is driven by a cam 111 disposed on an exhaust camshaft110, while a valve lift amount, a valve operation angle, and a valvetiming are kept constant.

On the other hand, a lift characteristic of intake valve 105 is variedby a VEL (variable operation angle mechanism) 112 and a TVC (variablevalve timing mechanism) 113.

VEL 112 is a mechanism that continuously varies the valve operationangle of intake valve 105 together with the valve lift amount thereof,namely, if the valve operation angle is increased, the valve lift amountis also increased in response to the increase in the valve operationangle, at the same time.

VTC 113 is a mechanism that varies a rotating phase of an intakecamshaft 13 relative to a crankshaft 120, to thereby continuously vary aphase of the valve operation angle of intake valve 105 relative tocrankshaft 120.

ECM 114 having a built-in micro computer sets a fuel injection amount(injection pulse width), an ignition timing, a target intake air amount,a target intake pipe negative pressure, and the like by performingcomputation processes according to a previously-stored program, and ECM114 outputs control signals to fuel injection valve 131, a powertransistor for a spark coil (not shown in the figures), electronicallycontrolled throttle 104, VEL 112, VTC 113, and the like, based on theseset values.

ECM 114 receives detection signals from a various kinds of sensors.

As the various sensors, there are disposed an air flow sensor 115 thatdetects an intake air amount QA of engine 101, an accelerator pedalsensor 116 that detects an opening degree ACC of an accelerator pedal139 operated by a driver of a vehicle, a crank angle sensor 117 thatoutputs a unit crank angle signal POS at each unit crank angle, athrottle sensor 118 that detects an opening degree TVO of throttle valve103 b, a water temperature sensor 119 that detects a cooling watertemperature TW of engine 101, a cam sensor 132 that outputs a cam signalCAM at each reference position of intake camshaft 13, an angle sensor133 that detects a rotating angle CSA of a control shaft 30 constitutingVEL 112, an atmospheric pressure sensor 135 that detects an atmosphericpressure AP, an intake pressure sensor 136 that detects an intakepressure PB on the downstream of throttle valve 103 b, an air-fuel ratiosensor 137 that is disposed on the upstream side of front catalyticconverter 108 and detects an air-fuel ratio AF based on an oxygenconcentration of an exhaust gas, and the like.

Unit crank angle signal POS is set so that a few, for example, one ortwo, lacks of unit crank angle signal POS occur at every crank anglecorresponding to the ignition timing among cylinders. The lackingposition of unit crank angle signal POS is detected according to anoutput cycle of unit crank angle signal POS, and a reference crank angleposition REF is detected based on the lacking position.

Based on a phase difference between cam signal CAM output from camsensor 132 and reference crank angle position REF, an advance amount ofthe valve timing operated by VTC 113 is detected.

Furthermore, a rotating speed NE of engine 101 is calculated based on adetection cycle of reference crank angle position REF or the number ofgenerated unit crank angle signal POS per unit time.

Next, the structure of VEL 112 will be described in detail withreference to FIGS. 2 through 6.

VEL 112 is provided with: a pair of intake valves 105, 105 slidablydisposed on a cylinder head 11; a hollow intake camshaft 13 rotatablysupported on the top of cylinder head 11; a drive cam 15 secured tointake camshaft 13 by press-fitting or the like; a pair of oscillatingcams 17, 17 disposed coaxially with drive cam 15 and actuates each ofintake valves 105, 105 to open via valve lifters 16, 16; rocker arm 18,one end section 18 a of which is linked to drive cam 15 via a link arm19 and the other end section 18 b of which is linked to oscillating cams17, 17 via a link member 20; a support arm 21, a base end section 21 aof which is rotatably supported on intake camshaft 13 and a tip endsection 21 b of which is coupled to a swing support of rocker arm 18;and drive means 22 that tilts support arm 21 for an angle within apredetermined angle range.

To intake camshaft 13, a rotating force is transmitted from crankshaft120 via a cam sprocket disposed on one end section of intake camshaft 13and a timing chain wounded around the cam sprocket.

As shown in FIG. 4, drive cam 15 includes a cam main body 15 a and acylindrical portion 15 b that is integrally provided on one outer endface of cam main body 15 a. An axial shaft insertion hole 15 c isinternally formed in drive cam 15, and the central axis “X” of cam mainbody 15 a is decentered by a predetermined amount from the central axis“Y” of intake camshaft 13.

Furthermore, drive cam 15 is fixed to intake camshaft 13 bypress-fitting, via shaft insertion hole 15 c.

Link arm 19 is provided with a base section 19 a and a protruding end 19b that is provided so as to protrude on the outer circumferential faceof base section 19 a. In the center position of base section 19 a thereis formed a fitting hole 19 c that rotatably fits with the outercircumferential face of cam main body 15 a of drive cam 15, and inprotruding end 19 b there is through-formed a pin hole 19 d throughwhich pin 23 for linking rocker arm 18 is rotatably inserted thereby.

As shown in FIGS. 3 and 4, oscillating cams 17, 17 are disposed on bothends of a cylindrical base section 17 a, in which there isthrough-formed a supporting hole 17 b through which intake camshaft 13is insert-fitted and rotatably supported.

In an end section 24 of one of oscillating cams 17, there isthrough-formed a pin hole 24 a.

Moreover, on the under face of each of oscillating cams 17, 17, thereare formed a base circular face 25 a and a cam face 25 b that extends inan arc shape from base circular face 25 a towards an end section 29side. Base circular face 25 a and cam face 25 b are to come in contactwith predetermined positions on the top face of each of valve lifters 19according to the oscillating position of oscillating cam 17.

A rotating direction of oscillating cams 17, 17 during a curveindicating lift-rise and extending from base circular face 25 a to theend edge of cam face 25 b is set to a direction opposite to a rotatingdirection of intake camshaft 13.

A bearing 14 includes a main bracket 14 a that supports base section 17a positioned between oscillating cams 17, 17, and a sub bracket 14 bthat rotatably supports control shaft 30 described later, and bothbrackets 14 a and 14 b are fastened to be fixed together from above by apair of bolts 14 c, 14 c.

As shown in FIG. 4, rocker arm 18 is arranged such that a central basesection 18 c is rotatably coupled to tip end section 21 b of support arm21 via a pin 26, one end section 18 a is rotatably coupled to protrudingend 19 b of link arm 19 via pin 23, and the other end section 18 b isrotatably coupled to one end section 20 a of link member 20 via a pin27.

As shown in FIG. 4, both end sections 20 a and 20 b of link member 20are rotatably coupled to the other end section 18 b of rocker arm 18 andend section 24 of oscillating cam 17, via pins 27 and 28, respectively.

Moreover, as shown in FIG. 2, a line Z1 extending from the rotationcenter point of oscillating cam 17 to the center point of the couplingof oscillating cam 17 and link member 20, and a line Z2 extending fromthe coupling center point and extending along the central axis of linkmember 20, are arranged to meet at a predetermined angle θ.

As shown in FIGS. 2 and 4, support arm 21 is arranged such that base endsection 21 a is rotatably supported on the outer circumferential face ofintake camshaft 13 via shaft insertion hole 21 c formed in base endsection 21 a, and tip end section 21 b is coupled to pin hole 18 d ofbase section 18 c of rocker arm 18 via pin 26, as described above, tothereby serve as the swing support of rocker arm 18.

Moreover, support arm 21 is arranged in a manner that base end section21 a is held between drive cam 15 and oscillating cam 17.

Furthermore, support arm 21 is configured to rotate upward and downwardby drive means 22, to thereby vary the valve lift amount of intakevalves 105, 105, and is set so that when the valve lift amount iscontrolled to decrease, the rotating direction of the support arm 21rotates downward in the direction same as the rotating direction ofintake camshaft 13, as indicated by an arrow in the figure.

Drive means 22 comprises control shaft 30 that is rotatably bornebetween main bracket 14 a and sub bracket 14 b of bearing 14, a controlcam 31 that is integrally secured on the outer circumference of controlshaft 30, a control link 32 by which control cam 31 and support arm 21are linked to each other, and a not-shown actuator that rotation-drivescontrol shaft 30.

As the actuator, an electric motor, for example, may be employed.

Each control cam 31 is secured on the outer circumference of controlshaft 30, and as shown in FIG. 2, a central axis P1 of control cam 31 isshifted from a central axis P of control shaft 30 by α.

Moreover, control link 32 is configured that one end section 32 athereof is rotatably supported on the outer circumferential face ofcontrol cam 31 via a circular hole 32 a, and the other end section 32 bthereof is rotatably coupled to support arm 21 on a substantially centerposition in the longitudinal direction of support arm 21 via a pin 33.

A rotating range of control shaft 30 is limited by a stopper so that thestopper permits control shaft 30 to rotate within an angle range from anangle position corresponding to a minimum valve lift amount/minimumvalve operation angle (default angle) to an angle position correspondingto a maximum valve lift amount/maximum valve operation angle. Controlshaft 30 is rotation-driven within the rotating range by the actuator,which is operated in response to a control signal provided from ECM 114.

In the followings, the operation of VEL 112 having the above describedstructure will be described.

First, to decrease the valve lift amount of intake valve 105, the angleposition of control shaft 30 is controlled so that central axis P1 ofcontrol cam 31 is positioned on the lower left side of central axis P2of control shaft 30 and a thick-walled part 31 a approaches intakecamshaft 13, as shown in FIG. 2.

At this time, support arm 21 downwardly rotates around base end section21 a and is maintained at a substantially horizontal position, as shownin the same figure.

Consequently, rocker arm 18 moves downward as a whole, and end section24 of each oscillating cam 17 is forcibly pulled up slightly via linkmember 20, so that oscillating cam 17 rotates leftward(counterclockwise) as a whole.

When one end section 18 a of rocker arm 18 is pushed up or down via linkarm 19 by a rotating movement of drive can 15, rocker arm 18 swingsabout tip end section 21 b of support arm 21 as a swing support. Theswing force is transmitted from the other end section 18 b tooscillating cam 17 and valve lifter 16 via link member 20, so that alift amount L1 becomes relatively small as shown in FIG. 5.

Thus, as shown in FIG. 7, when the valve lift amount and the valveoperation angle are decreased, the phase of the center angle position ofthe valve operation angle relative to crankshaft 120 thereof (i.e.,center phase) varies in a retard direction compared with that of whenthe valve lift amount and the valve operation angle are larger.

In contrast, to increase the valve lift amount and the valve operationangle, control shaft 30 is rotation-driven so that control cam 31 isrotated clockwise by approximately 180° from the position indicated inFIGS. 2 and 5 and central axis P1 (thick-walled part 31 a) is movedupward, as shown in FIGS. 6A and 6B.

At this time, support arm 21 upwardly rotates around base end section 21a and is maintained at a rotated position with a predetermined angle.Rocker arm 18 moves upward as a whole, and the other end section 18 b ofrocker arm 18 presses upper end section 24 of oscillating cam 17 in arightward direction in the illustration of FIG. 2 via link member 20, sothat oscillating cam 17 rotates clockwise by a predetermined degree as awhole.

Thus, as shown in FIG. 6A, cam face 25 b of oscillating cam 17 comes incontact with a top face of valve lifter 16, and when one end section 18a of rocker arm 18 is pushed up via link arm 19, a lift amount L2becomes larger, as shown in FIG. 6B.

Namely, as shown in FIG. 7, when the valve lift amount and the valveoperation angle are larger, the phase of the center angle position ofthe valve operation angle relative to crankshaft 120 thereof (i.e.,center phase) varies in an advance direction compared with that of whenthe valve lift amount and the valve operation angle are smaller.

As mentioned above, in VEL 112, to decrease the valve lift amount andthe valve operation angle, support arm 21 is rotated from the upperrotated position as shown in FIGS. 6A and 6B to the horizontal rotatedposition as shown in FIGS. 2 and 5. This rotating direction is the sameas the rotating direction of intake camshaft 13 and is the directionopposite to the rotating direction of the lift-rise of oscillating cam17. Accordingly, the center phase of the valve operation angle of intakevalves 105, 105 is retarded as shown in FIG. 7.

Thus, to decrease the valve lift amount and the valve operation angle,support arm 21 is rotated downward by the downwardly rotating movementof control cam 31, as described above. At this time, driving cam 15 alsorotates in the same direction. Thus a time required for operating from aposition after the top dead center to a position where the liftingstarts becomes longer, and accordingly, a swing start timing of rockerarm 18 is also delayed.

On the other hand, since the rotating direction of support arm 21 is setto be opposite to the rotating direction of oscillating cam 17 duringthe lift-rise, a delay in the lift-rising timing of oscillating cam 17occurs due to the delay in the swing start timing of rocker arm 18.Consequently, when the valve lift amount and the valve operation angleare decreased, the center phase of the valve operation angle isretarded, as shown in FIG. 7.

In the present embodiment, the center phase of the valve operation anglehas characteristics that the center phase is retarded when the valvelift amount and the valve operation angle is changed to be smaller.However, the center phase may have characteristics that the center phaseis advanced, contrary to the present embodiment.

FIG. 8 shows a structure of VEL 112 in which the variationcharacteristics of the center phase in response to the variation in thevalve lift amount and the valve operation angle, is opposite to that inthe mechanism shown in FIGS. 2 through 6.

The structure of VEL 112 shown in FIG. 8 is basically the same as thatshown in FIGS. 2 though 6, except that the rotating direction of supportarm 21 relative to the rotating direction of intake camshaft 13 is setto be opposite to the direction set in the mechanism of FIGS. 2 through6 when the valve lift amount and the valve operation angle aredecreased, and that oscillating cam 17 is reversely arranged so that therotating direction of oscillating cam 17 during the lift-rise is thesame as the rotating direction of intake camshaft 13.

Namely, the rotating direction of oscillating cam 17 during thelift-rise in VEL shown in FIG. 8 is set to be opposite to the rotatingdirection of support arm 21.

Thus, to decrease valve lift amount and the valve operation angle,support arm 21 is rotate upward by drive means 22, so that rocker arm 18also moves upward. At this time, since drive cam 15 rotates in adirection opposite to this movement, a rocking timing of rocker arm 18becomes earlier.

Consequently, the rotating movement of oscillating cam 17 in alift-rising direction becomes earlier, and accordingly, if the valvelift amount and valve operation angle are decreased, the center phase ofthe valve operation angle is advanced at the same time, as shown in FIG.9.

ECM 114 receives a detection signal provided from angle sensor 133 thatdetects the rotating angle of control cam 30, and in order to rotatecontrol shaft 30 to a target angle position corresponding to a targetvalve operation angle/target valve lift amount, ECM 133 feedbackcontrols a manipulated variable of the actuator that rotates controlshaft 30 based on the detection result of angle sensor 133.

Next, the structure of VTC 113 will be described with reference to FIG.10.

Although a vane-type variable valve timing mechanism is employed as VTC113 in the present embodiment, VTC 113 is not limited to the vane-typemechanism, and various known mechanisms, such as an electric mechanismand a mechanism using an electromagnetic retarder, may be adopted.

Vane-type VTC 113 is provided with a cam sprocket 51 that isrotation-driven by crank shaft 120 via a timing chain, a rotation member53 that is fixed on the end section of intake camshaft 13 and rotatablyhoused within cam sprocket 51, a hydraulic circuit 54 that relativelyrotates rotation member 53 with respect to cam sprocket 51, and alocking mechanism 60 that selectively locks the relative rotationalposition between cam sprocket 51 and rotation member 53 in apredetermined position.

Cam sprocket 51 comprises: a rotating section (not shown in the figure)having a teeth section on the outer circumference thereof, with whichthe timing chain meshes; a housing 56 that is disposed in front of therotating section so as to rotatably house rotation member 53; and afront cover and a rear cover (not shown in the figure) that blockfront/rear openings of housing 56.

Housing 56 is of a cylindrical shape, with both of the front/rear endsformed open ended, and on the inner circumferential face of housing 56there are provided four protruding partition wall sections 63 insectionally trapezoid shape along the circumferential direction ofhousing 56 at equal intervals of 90°.

Rotation member 53 is fixed to the front end section of intake camshaft13 and is provided with four vanes 78 a, 78 b, 78 c, 78 d formed thereinat equal intervals of 90° on the outer circumferential face of anannularly extended base section 77.

First to fourth vanes 78 a to 78 d are respectively of substantiallysectionally inverse trapezoid shape and are disposed in cavity sectionsbetween respective partition wall sections 63, and they partition thesecavity sections in front and rear thereof in the rotating direction.Thereby, between both sides of vanes 78 a to 78 d and both end faces ofthe respective partition wall sections 63, there are formed an advanceangle side hydraulic pressure chamber 82 and a retard angle sidehydraulic pressure chamber 83.

Locking mechanism 60 is configured such that a lock pin 84 isinsert-fitted into an engaging hole (not shown in the figure) in arotating position on the maximum retard angle side of rotation member 53(in a default position).

Hydraulic circuit 54 has two systems of oil pressure passages, namely afirst oil pressure passage 91 that supplies and discharges oil pressureto advance angle side hydraulic pressure chamber 82 and a second oilpressure passage 92 that supplies and discharges oil pressure to retardangle side hydraulic pressure chamber 83, and to both of these oilpressure passages 91 and 92, there are connected a supply passage 93 anddrain passages 94 a and 94 b respectively via an electromagneticswitching valve 95 for switching the passages.

In supply passage 93, there is provided an engine-driven oil pump 97that pressure feeds the oil inside an oil pan 96, while the downstreamside ends of drain passages 94 a and 94 b are communicated with oil pan96.

First oil pressure passage 91 is connected to four branched passages 91d that are formed in a substantially radial pattern in base section 77of rotation member 53 so as to communicate with the respective advanceangle side hydraulic pressure chambers 82, and second oil pressurepassage 92 is connected to four oil holes 92 d that open to respectiveretard angle side hydraulic pressure chambers 83.

Electromagnetic switching valve 95 is configured such that a spool valvetherein carries out relative switching control between respective oilpressure passages 91 and 92, supply passage 93, and drain passages 94 aand 94 b.

ECM 114 controls a current flow amount to an electromagnetic actuator 99that drives electromagnetic switching valve 95, based on a duty controlsignal.

For example, when a control signal of a duty ratio of 0% (OFF signal) isoutput to electromagnetic actuator 99, the operating oil that has beenpressure-fed from oil pump 97 travels through second oil pressurepassage 92 to be supplied into retard angle side hydraulic pressurechamber 83, and the operating oil within advance angle side hydraulicpressure chamber 82 travels through first oil pressure passage 91 to bedischarged from first drain passage 94 a into oil pan 96.

Consequently, the internal pressure of retard angle side hydraulicpressure chamber 83 becomes high and the internal pressure of advanceangle side hydraulic pressure chamber 82 becomes low, and rotationmember 53 rotates towards the retard angle side via vanes 78 a to 78 d.As a result, the phase of the opening timing of intake valve 105relative to crankshaft 120 is retarded.

On the other hand, when a control signal of a duty ratio of 100% (ONsignal) is output to electromagnetic actuator 99, the operating oiltravels through first oil pressure passage 91 so as to be supplied intoadvance angle side hydraulic pressure chamber 82, and the operating oilwithin retard angle side hydraulic pressure chamber 83 travels throughsecond oil pressure passage 92 and second drain passage 94 b so as to bedischarged into oil pan 96, thereby reducing the pressure of retardangle side hydraulic pressure chamber 83.

Therefore, rotation member 53 rotates towards the advance angle side viavanes 78 a to 78 d, thereby advancing the phase of the opening timing ofintake valve 105 relative to crankshaft 120.

Thus, within a range where vanes 78 a to 78 d can relatively rotate inhousing 56, the phase of intake camshaft 13 relative to crankshaft 120continuously shifts between the most retarded position and the mostadvanced position, and the phase of the opening timing of intake valve105 continuously shifts.

In the followings, the control operation of VEL 112 and VTC 113 cardedout by ECM 114 will be described in detail, with reference to theflowchart shown in FIG. 11.

A routine indicated in the flowchart of FIG. 11 is executed at everygiven fixed cycle (e.g., 10 microseconds each).

In step S501, a target torque is calculated based on both acceleratoropening degree ACC detected by accelerator pedal sensor 116 and enginerotating speed NE calculated based on the signal from crank angle sensor117.

As shown in FIG. 12, the target torque is calculated by making referenceto a previously-provided map, in which there is previously stored thetarget torque employing accelerator opening degree ACC and enginerotating speed NE as variables.

Here, the target torque is set so that the larger accelerator openingdegree ACC is or the greater engine rotating speed NE is, the largertarget torque is calculated.

In the next step S502, each of a target value of the valve operationangle (target operation angle) that is varied by VEL 112 and a targetadvance amount in VTC 113 is calculated from the target torque andengine rotating speed NE.

Here, the target advance amount is expressed as an advance angle fromthe most retarded position which is a reference position (defaultposition), and the target operation angle is calculated as a rotatingangle from a reference angle (default angle) of control shaft 30 thatcorresponds to the minimum valve operation angle.

As shown in FIG. 13, there is provided a map which previously stores thetarget operation angle by employing the target torque and enginerotating speed NE as variables and thus, a given target operation angleis calculated by making reference to the previously-provided map. Here,it should be understood that the larger the target torque is or thegreater engine rotating speed NE is, the larger target operation angleis calculated.

Moreover, as shown in FIG. 14, there is provided a map which previouslystores the target advance amount by employing the target torque andengine rotating speed NE as variables and thus, a given target advanceamount is calculated by making reference to the previously-provided map.Here, as shown in FIG. 14, in a region where the engine rotation is low,the target advance amount is set to the most advanced value in areference operation region which is near the center of the low rotationregion, and as separating from the reference operation region, thetarget advance amount is more retarded. Furthermore, in the highrotation region, the target advance amount is set to a value in a moreretard angle side than that in the low rotation region, and as enginerotating speed NE gets higher, the target advance amount is retarded.

The target operation angle and target advance amount, however, may beset based on any engine operating state, and not limited to theconfiguration in which the target operation angle and target advanceamount are set based on the target torque and engine rotating speed NE.

The target advance amount is calculated as a target of the center phaseof the valve operation angle of intake valve 105.

However, VEL 112 employed in the present embodiment is a mechanism inwhich the center phase of the valve operation angle varies in responseto an increase/decrease in the valve operation angle, as describedabove. Accordingly, even if VTC 113 is controlled to the most retardedposition, an actual center phase will differ from the target centerphase depending on the valve operation angle at that time, for example.

Thus, in the next step S503, a correction value for correcting thetarget advance amount based on a change amount of the center phasecaused by the variation in the valve operation angle varied by VEL 112.

Specifically, there is previously provided a table in which thecorrection value according to the target operation angle is stored, andin step S503, the correction value corresponding to the target operationangle at that time is retrieved from the table.

Here, as shown in FIG. 7, if there is employed VEL 112 which retards thecenter phase in response to the decrease in the valve operation angle,the center phase is advanced as the valve operation angle increases,when using a center phase of the minimum valve operation angle as abasis.

Then, in order to cancel out the advancing change of a center phase dueto the increase in the valve operation angle so as to conform the centerphase of the increased valve operation angle to a center phase of theminimum operation angle, the correction value is set, as shown in FIG.15 by a dotted line, to a value that: is a negative number, an absolutevalue of which increases as the target operation angle increases; andcorrects the target advance amount in the retard direction to a greaterdegree as the target operation angle increases.

On the other hand, as shown in FIG. 9, if there is employed VEL 112which advances the center phase in response to the decrease in the valveoperation angle, the center phase is retarded as the valve operationangle increases, when using the center phase of the minimum valveoperation angle as a basis.

Thus, in order to cancel out the retarding change of a center phase dueto the increase in the valve operation angle so as to conform the centerphase of the increased valve operation angle to a center phase of theminimum operation angle, the correction value is set, as shown in FIG.15 by a solid line, to a value that: is a positive number, an absolutevalue of which increases as the target operation angle increases; andcorrects the target advance amount in the advance direction to a greaterdegree as the target operation angle increases.

In step S504, the target advance amount set in step S502 is added withthe correction value set in step S503, thereby obtaining a final targetadvance amount.

By controlling VTC 113 based on the final target advance amountcorrected with the correction value, even if the target valve operationangle differs, the center phase at that time can be controlled to acenter phase required from the target torque and engine rotating speedNE at that time.

In step S505, a manipulated variable of VEL 112 is feedback controlledbased on the target operation angle set in step S502, and a manipulatedvariable of VTC 113 is feedback controlled based on the final targetadvance amount corrected in step S504.

For these feedback controls, various control techniques, such as a PIDcontrol that sets a proportional manipulated variable, an integralmanipulated variable and a derivative manipulated variable, a referencemodel control, a sliding mode control, and the like, may be used basedon a difference between a control amount detected by a sensor and atarget value.

In a first embodiment indicated in the flowchart shown in FIG. 11, thecorrection value for correcting the target advance amount is obtained byretrieving from the table based on the target operation angle, however,the correction value may be set by calculating the change amount of thecenter phase due to the varied valve operation angle from the targetoperation angle at that time. In the followings, a second embodimentaccording this configuration will be described with reference to theflowchart shown in FIG. 16.

In steps S601 and S602, a target torque, a target operation angle, and atarget advance amount are calculated as with the above steps S501 andS502.

In step S603, a difference between a central phase at the targetoperation angle at that time and a central phase at a referenceoperation angle (minimum operation angle), and based on the obtaineddifference, the correction value is set.

Specifically, an opening timing IVO and a closing timing IVC of intakevalve 105 in the target operation angle at that time and in the casewhere VTC 113 is controlled to a reference advance amount, is calculatedin accordance with the following equation:

IVO=IVOdef−(OPAtar−OPAdef)×RIVO

IVC=IVCdef+(OPAtar−OPAdef)−(1−RIVO)

Here, the opening/closing timings of intake valve 105 are expressed as aretard angle from the top dead center.

In the above equation, OPAtar is a target operation angle, and OPAdef isan operation angle in a default state of VEL 112 (reference operationangle), e.g., a minimum operation angle.

IVOdef is an opening timing IVO in the default state of VEL 112 and VTC113, namely, in the minimum operation angle and the most retardedposition, and IVCdef is a closing timing IVC in the default state of VEL112 and VTC 113, namely, in the minimum operation angle and the mostretarded position. These IVOdef and IVCdef are previously stored.

Furthermore, RIVO represents a ratio of a change angle of opening timingIVO to a change amount of the valve operation angle operated by VEL 112,and RIVC represents a ratio of a change angle of closing timing IVC to achange amount of the valve operation angle operated by VEL 112.

Here, RIVO+RIVC=100%.

For example, in the case where the center phase of valve operation angledoes not vary even the valve operation angle is varied by VEL 112,opening timing IVO is advanced for a half of increased angle of thevalve operation angle, and closing timing IVC is retarded for the otherhalf of increased angle, and similarly, opening timing IVO is retardedfor a half of decreased angle of the valve operation angle, and closingtiming IVC is advanced for the other half of decreased angle.

Thus, in the case where the center phase of valve operation angle doesnot vary even the valve operation angle is varied because opening timingIVO varies for a half of the change angle of the valve operation angleand closing timing IVC varies for the other half of the change angle ofthe valve operation angle, ratio RIVO and ratio RIVC become 50%.

On the other hand, as in VEL 112 of the present embodiment, in the caseof such a mechanism that the center phase is simultaneously varied byvarying the valve operation angle, when the center phase is retarded inresponse to the increase of valve operation angle as shown in FIG. 9, anangle change amount of closing timing IVC with respect to the change inthe valve operation angle becomes larger than an angle change amount ofopening timing IVO, and accordingly, ratio RIVO becomes less than 50%.

In other words, in the case where opening timing IVO varies for an angleless than half of the change amount of the valve operation angle andclosing timing IVC varies for an angle more than half of the changeamount of the valve operation angle, the center phase is retarded inresponse to the increase in the valve operation angle, and thus, ratioRIVO at that time becomes 0% S RIVO<50%.

Furthermore, ratio RIVO of 0% indicates a characteristic that openingtiming IVO is constant (i.e., does not vary) while the valve operationangle is varied, and the valve operation angle varies by varying dosingtiming IVC.

For example, when opening timing IVO is advanced for an anglecorresponding to 30% of the increased amount of valve operation angleand closing timing IVC is retarded for an angle corresponding to 70% ofthe same, ratio RIVO is 30% and ratio RIVC is 70%.

In contrast, when the center phase is advanced in response to theincrease in the valve operation angle as shown in FIG. 7, an anglechange amount of closing timing IVC with respect to the change in thevalve operation angle becomes smaller than an angle change amount ofopening timing IVO, and accordingly, ratio RIVO becomes more than 50%.

In other words, in the case where opening timing IVO varies for an anglemore than half of the change amount of the valve operation angle andclosing timing IVC varies for an angle less than half of the changeamount of the valve operation angle, the center phase is advanced inresponse to the increase in the valve operation angle, and thus, ratioRIVO at that time becomes 50% <RIVO≦100%.

Furthermore, ratio RIVO of 100% indicates a characteristic that closingtiming IVC is constant (i.e., does not vary) while the valve operationangle is varied, and the valve operation angle varies by varying openingtiming IVO.

Because ratios RIVO and RIVC are fixed values which is determineddepending on the structure/specification of VEL 112, ratio RIVO and/orratio RIVC is previously stored.

Moreover, “OPAtar−OPAdef” is an increased amount of the target operationangle with respect to the minimum operation angle, and“(OPAtar−OPAdef)×RIVO” is a change angle of opening timing IVOcorresponding to the increased amount. Still further, since “1−RIVO” isequal to RIVC, “(OPAtar−OPAdef)×(1−RIVO)” indicates a change angle ofclosing timing IVC corresponding to the increased amount of the targetoperation angle with respect to the minimum operation angle.

Here, IVOdef is opening timing IVO in the default state, and IVCdef isclosing timing IVC in the default state. In VEL 112 of the presentembodiments, the center phase is retarded in response to the increase invalve operation angle.

Accordingly, “IVOdef−(OPAtar−OPAdef)×RIVO” indicates opening timing IVOthat is advanced by varying the valve operation angle from the minimumvalue to the target value in the state where VTC 113 is fixed to themost retarded angle side. Further, “IVC def+(OPAtar−OPAdef)×(1−RIVO)”indicates closing timing IVC that is retarded by varying the valveoperation angle from the minimum value to the target value in the statewhere VTC 113 is fixed to the most retarded angle side.

After obtaining opening timing IVO and closing timing IVC at the targetoperation angle, as indicated above, the correction value for correctingthe target advance amount is calculated in accordance with the followingequation:

Correction value=(IVO+IVC)/2−SPdef

In this equation, “(IVO+IVC)/2” indicates an angle from the top deadcenter to the center phase at the target operation angle. Similarly,SPdef indicates an angle from the top dead center to the center phase inthe default state of VEL 112 and VTC 113.

Thus, by correcting the target advance amount by the correction value, acenter phase can be controlled to the target center phase even if thecenter phase varies in response to the variation in the valve operationangle.

For example, as shown in FIG. 9, in VEL 112 in which the center phase isretarded as the target operation angle increases, if a default operationangle (reference operation angle) is the minimum operation angle, thepositive correction value, the absolute value of which increases as thetarget operation angle increases, can be set similarly to thecharacteristics shown in FIG. 15 by the solid line.

In contrast, as shown in FIG. 7, in VEL 112 in which the center phase isadvanced as the target operation angle increases, if a default operationangle (reference operation angle) is the minimum operation angle, thenegative correction value, the absolute value of which increases as thetarget operation angle increases, can be set similarly to thecharacteristics shown in FIG. 15 by the solid line.

After calculating the correction value, as indicated above, in the nextstep S604 the target advance amount obtained in step S602 is correctedby the correction value, thereby obtaining a final target advanceamount.

Then, in the next step S605, VEL 112 is feedback controlled based on thetarget operation angle that is set in step S602, and VTC 113 is feedbackcontrolled based on the final target advance amount corrected in stepS604.

In the followings, calculation of the correction value in step S603 willbe described in more specific, with reference to FIG. 17.

FIG. 17 shows the case where the open characteristics of intake valve105 is changed from that in the default state to the valvecharacteristics at an intermediate-load operation.

As used herein, the intermediate-load operation means a constant-speedoperating state at vehicle speed of approximately 40 km/h and anoperating state in which low-fuel consumption is required.

The default state of VEL 112 is a state having the minimum operationangle as described above, and the default state of VTC 113 is a statehaving the most retarded angle, and accordingly, the center phase at theminimum operation angle/the most retarded angle, and opening timing IVOand closing timing IVC at the minimum operation angle/the most retardedangle position are previously stored.

Here, in the default state, the valve operation angle is set to 68 deg,opening timing IVO is set to 84 degree ATDC (after top-dead-center)(hereinafter, referred to as “deg ATDC”), closing timing IVC is set to152 deg ATDC, and the center phase is set to 118 deg ATDC.

Then, for the intermediate-load operation time, the target advanceamount is set to 52 deg, and the target operation angle is set to 100deg. Herein, as an example, the case where the center phase of 66 degATDC at the valve operation angle of 100 deg is achieved will bedescribed.

If VEL 112 is a mechanism that can vary the valve operation anglewithout varying the center phase, the center phase does not varies evenwhen only the valve operation angle is varied, and thus, by controllingVTC 113 based on the target advance amount, the target center phase canbe obtained.

However, as in the present embodiment, in VEL 112 that varies the centerphase to be retarded in response to the increase in the valve operationangle, the center phase might include a difference from the target anglefor the change amount of the center phase operated by VEL 112 unless thetarget advance amount is corrected for the change amount of the centerphase operated by VEL 112. Thus, the correction value is calculated fromthe following equation:

IVO=IVOdef−(OPAtar−OPAdef)×RIVO

IVC=IVCdef+(OPAtar−OPAdef)×(1−RIVO)

Correction value=(IVO+IVC)/2−SPdef

In the example of FIG. 13, opening timing IVO, closing timing IVC,correction value can be calculated as follows. Here, the ratio RIVO isset to be 30%.

$\begin{matrix}{{IVO} = {{84\mspace{14mu} \deg} - {( {{100\mspace{14mu} \deg} - {68\mspace{14mu} \deg}} ) \times 30\%}}} \\{= {74.4\mspace{14mu} \deg}}\end{matrix}$ $\begin{matrix}{{IVC} = {{152\mspace{14mu} \deg} + {( {{100\mspace{14mu} \deg} - {68\mspace{14mu} \deg}} ) \times ( {{100\%} - {30\%}} )}}} \\{= {174.4\mspace{14mu} \deg}}\end{matrix}$ $\begin{matrix}{{{Correction}\mspace{14mu} {value}} = {{( {{74.4\mspace{14mu} \deg} + {174.4\mspace{14mu} \deg}} )/2} - {118\mspace{14mu} \deg}}} \\{= {6.4\mspace{14mu} \deg}}\end{matrix}$

The above “(74.4 deg+174.4 deg)/2”, from which the correction value canbe calculated, indicates the center phase that varies due to theincrease in the valve operation angle from the minimum 68 deg to 100 degwhile maintaining VTC 113 to be in the most retarded state, and thecorrection value at that time indicates the retard change amount of thecenter phase of when the operation angle is varied from 68 deg (i.e.,the minimum value) to 100 deg by VEL 112.

On the other hand, the target advance amount of 52 deg is such a targetvalue that it is set by assuming that the center phase does not varyeven the valve operation angle varies. Thus, if the center phase isretarded for 6.4 deg by setting the target operation angle to 100 deg,the starting point of advancing operation is position to be moreretarded, and accordingly, it becomes necessary to set the targetadvance amount to a value on the advanced side for extra 6.4 deg inaddition to 52 deg.

Consequently, by setting the target advance amount as the sum of 52 degand 6.4 deg, 66 deg ATDC, which is the target center phase, can beachieved.

FIG. 18 shows the change of open characteristics of intake valve 105 ofwhen the operating state is changed from the intermediate-load operationin which the target operation angle is set to 100 deg and the targetcenter phase is set to 66 deg ATDC to the operating state where theaccelerator pedal is fully operated.

Here, since the accelerator pedal is fully operated, the target centerphase is changed from 66 deg ATDC to 98 deg ATDC. In accordance withthis change, the target advance amount of VTC 113 is changed from 52 degto 20 deg, and the target operation angle at the state where theaccelerator pedal is fully operated (WOT) is set to 240 deg.

Under these conditions, opening timing IVO, dosing timing IVC,correction value can be calculated as follows.

$\begin{matrix}{{IVO} = {{84\mspace{14mu} \deg} - {( {{240\mspace{14mu} \deg} - {68\mspace{14mu} \deg}} ) \times 30\%}}} \\{= {32.4\mspace{14mu} \deg}}\end{matrix}$ $\begin{matrix}{{IVC} = {{152\mspace{14mu} \deg} + {( {{240\mspace{14mu} \deg} - {68\mspace{14mu} \deg}} ) \times ( {{100\%} - {30\%}} )}}} \\{= {272.4\mspace{14mu} \deg}}\end{matrix}$ $\begin{matrix}{{{Correction}\mspace{14mu} {value}} = {{( {{32.4\mspace{14mu} \deg} + {272.4\mspace{14mu} \deg}} )/2} - {118\mspace{14mu} \deg}}} \\{= {34.4\mspace{14mu} \deg}}\end{matrix}$

Thus, in the case where the operating state is changed from the statewhere the target operation angle is 100 deg and the target center phaseis 66 deg ATDC to the state where the accelerator pedal is fullyoperated, the target center phase can be achieved by correcting thetarget advance amount of 20 deg to 54.4 deg.

Thus, even if the target advance amount, which is set relative to thetarget torque and the engine rotating speed, is set as an advance amountfrom the center phase at the default state, the center phase can becontrolled to achieve the target center phase with high precision byusing the correction value.

FIG. 19 shows a flowchart indicating a third embodiment of the presentinvention, in which a failsafe control is executed in the case where anabnormality has occurred in VEL 112, while performing correction of thetarget advance amount as shown in the flowchart of FIG. 11 or 16.

In step S701 of the flowchart of FIG. 19, it is diagnosed whether or nota failure of VEL 112 has occurred.

The failure diagnosis of VEL 112 is executed by a separate program (notshown in the figure). When it is determined that the failure hasoccurred, a failure determination flag is set at 1, and when it isdetermined that VEL 112 is normal, the failure determination flag is setat 0. Consequently, in the step S701, discrimination of failure/normalis performed by discriminating the failure determination flag.

As a failure of VEL 112, there is included an abnormality in operationcaused by a breaking or a short circuit of a power supply line and/ordriving signal line, a fixation of the driving portions due to a foreignmatter caught therebetween, and the like.

In particular, if the rotating phase is advanced by VTC 113 in the casewhere the valve operation angle and valve lift amount are large and VEL112 is unable to work, a valve lift amount near the top dead center of apiston might be abnormally large, and thus intake valve 105 and thepiston might interfere with each other.

Thus, if it is discriminated in step S701 that the failure of VEL 112has occurred, the flow proceeds to step S702 in order to avoid theoccurrence of the interference of piston, or the like.

The abnormality discriminated in step S701 may be limited to anabnormality that the valve operation angle and the valve lift amount arefixed to the larger value, or an abnormality that the valve lift amountis controlled to a larger value than a target value, to thereby set amain object of the failsafe control to an avoidance of pistoninterference.

In step S702, a target advance amount of VTC 113 is forcibly set to thea most retarded angle, and in the next step S703, a gain in a feedbackcontrol of VTC 113 is switched to a gain larger than that in the casewhere VEL 112 is normal, to thereby converge the actual advance amountto the target advance amount which is set to the most retarded angle,with good response.

In the case where the feedback control is executed by the proportionalplus integral action based on a control error, for example, theabove-mentioned gain is a proportional gain plus integral gain, andfurther, if it is discriminated that the failure of VEL 112 hasoccurred, the proportional gain plus integral gain is changed to thelarger value than that in the case where VEL 112 is normal.

Thus, even if the abnormality of the valve operation angle and the valvelift amount to be fixed to the larger value occurs in VEL 112, the valvelift amount near the top dead center can be set smaller by promptlyretarding the center phase of intake valve 105, and thus, theinterference between intake valve 105 and the piston can be avoided.

In contrast, if it is determined in step S701 that VEL 112 is normal,the flow proceeds to steps S704 through S707, and then a targetoperation angle and a target advance amount are determined as with theabove steps S501 through S504.

The setting process of a correction value in step S706 may be such aprocess that the correction value is set by being retrieved from a tablebased on the target operation angle as indicated in the above step S503,and further the process may be such a process that the correction valueis obtained by performing computation processes based on theopening/closing timing of intake valve 105 at the target operationangle.

In step S708, a value indicating a load variation of engine 101, such asa temporal derivative value ΔAPO of an accelerator opening degree APO,is calculated, and then a determination of a transient operation stateof engine 101 is performed.

In step S709, based on the value indicating the variation of engineload, such as the temporal derivative value ΔAPO of the acceleratoropening degree APO, a feedback gain of VTC 113 is set.

At this time, if the absolute value of the temporal derivative valueΔAPO is large and the engine is in an abrupt acceleration/decelerationstate, the feedback gain is set larger.

Consequently, at the transient operation of engine 101, closing timingIVC of intake valve 105 can be converged to the target with goodresponse, and a response to an intake air amount control can beimproved, and accordingly, a response of engine can be improved.

In step S710, VEL 112 and VTC 113 are feedback controlled based on atarget value and a control gain.

As described above in each embodiment, it will be apparent to thoseskilled in the art that the present invention can be adopted to eithertype of VEL 112, namely, such types that the center phase is eitheradvanced or retarded in response to the increase in the valve operationangle, and further, can be adopted to the case where a valve operationangle of an exhaust valve is varied.

In VEL 112 which is provided for varying the valve operation angle ofintake valve 105, however, it is preferable to employ thecharacteristics that the center phase is retarded in response to theincrease in the valve operation angle of intake valve 105, as shown inFIG. 9, and furthermore, it is preferable to set the above-mentionedratio RIVO to be 30%, as shown in FIG. 20.

By setting ratio RIVO to be 30%, a response at a transient operation,fuel-saving benefit at the transient operation, and an engine-stallresistance at engine cooling time and at engine deceleration time, canbe simultaneously achieved.

In the followings, effects obtained by setting ratio RIVO to be 30% willbe described in detail.

Regarding Improvement of Response at Transient Operation

As shown in FIG. 21, in order to achieve fuel-saving at a constant-speedoperation at a vehicle speed of 40 km/h, for example, it is desired toretard opening timing IVO of intake valve 105 to an angle after the topdead center, to thereby reduce valve overlap, so that a fresh air amountand a fuel injection amount are reduced, and it is also desired toadvance closing timing IVC of intake valve 105 to an angle before theintake bottom dead center, to thereby reduce a pumping loss.

On the other hand, when an acceleration requirement occurs, it ispreferable to increase the valve lift amount/valve operation angle ofintake valve 105 to increase the intake air amount, and to retardclosing timing IVC of intake valve 105 to an angle after the intakebottom dead center to improve a filling efficiency inside the cylinderby the inertia supercharging effect.

Thus, when the engine is accelerated from the steady state, a fastercontrol response of valve overlap amount is required, and moreparticularly, it is important to improve responsiveness of the retardchange of closing timing IVC of intake valve 105.

Here, as shown in FIG. 20, by employing VEL 112 having characteristicsthat the center phase is retarded in response to the increase in thevalve operation angle/valve lift amount of intake valve 105, the valveoperation angle of intake valve 105 is increased in response to theacceleration requirement, resulting that the center phase can besimultaneously retarded, and further, the phase can be operated in theretard direction by VTC 113.

Thus, since the retard change of the phase operated by VEL 112 and theretard change of the phase operated by VTC 113 simultaneously occur,response of retard change of closing timing IVC at the time ofacceleration becomes faster, and thus, closing timing IVC can beretarded to an angle after the intake bottom dead center and the inertiasupercharging effect can be obtained immediately, so that theacceleration response can be improved.

FIG. 22 shows the change in valve operation angle performed by VEL 112,the change in advance amount of phase operated by VTC 113, and thechange in opening timing IVO/closing timing IVC of intake valve 105, inthe case where the engine employing VEL 112 in which ratio RIVO is setto be 50% and the center phase does not vary while the valve operationangle is increased is used and where the operating state is changed fromthe constant-speed operation at immediate-lode to the operating statewhere the accelerator pedal is fully operated.

Furthermore, FIG. 23 shows the change in valve operation angle operatedby VEL 112, the change in advance amount of phase operated by VTC 113,and the change in opening timing IVO/closing timing IVC of intake valve105, in the case where the engine employing VEL 112 in which ratio RIVOis set to be 30% and the center phase varies to be retarded in responseto the increase in the valve operation angle is used and where theoperating state is changed from the constant-speed operation atimmediate-lode to the operating state where the accelerator pedal isfully operated.

In the case where ratio RIVO is set to be 50% as shown in FIG. 22(A),opening timing IVO and closing timing IVC vary at equal rate. Then, inorder to vary the center phase to the target, VTC 113 retards the phasefor 32 deg as shown in FIG. 22(B).

Accordingly, even when the valve operation angle reaches the target,closing timing IVC does not reach the target value until VTC 113completes to retard the phase for 32 deg. In this example, it takes 0.17sec to reach the target closing timing IVC (see FIG. 22(C)).

In contrast, in the case where ratio RIVO is set to be 30%, the centerphase is retarded in response to the increase in the valve operationangle, as shown in FIG. 23(A), and thus, the manipulated variable thatis needed to be retarded by VTC 113 can be reduced. In the example shownin FIG. 23(B), VTC 113 retards the phase for only 4 deg, therebyachieving closing timing IVC to reach the target value.

Thus, as shown in FIG. 23(C), since no delay in reaching the targetvalue as caused by the delay in response of VTC 113 occur, it takes only0.14 sec to reach the target closing timing IVC, which is faster thanthat in the case where ratio RIVO is set to be 50%.

Hence, by employing VEL 112 that retards the center phase in response tothe increase in the valve operation angle of intake valve 105, timebefore reaching the target closing timing IVC can be reduced and theinertia supercharging effect cam be obtained sooner, so that theresponse of acceleration can be improved.

FIG. 24 shows a diagrammatic view indicating the relationship betweenratio RIVO/RIVC and a response time of intake air amount.

In FIG. 24, the characteristics that ratio RIVO is set to be 0% andratio RIVC is set to be 100% are such characteristics that openingtiming IVO of intake valve 105 is constant and only dosing timing IVCvaries in order to vary the valve operation angle of intake valve 105 byVEL 112. The characteristics that both ratios RIVO and RIVC are set tobe 50% are such characteristics that the center phase does not vary evenwhen the valve operation angle is varied by VEL 112.

Each of the dotted line and the solid line in FIG. 24 indicates theresponse time of VTC 113 with different response speeds. The dotted lineindicates the characteristics that have relatively slow response speedand the characteristics of the vane-type variable valve timing mechanismemployed in the present embodiment.

As ratio RIVO approaches 50%, the retard manipulated variable requiredby VTC 113 becomes large. Thus, as shown in FIG. 24 by the dotted line,if VTC 113 has slower response speed and if ratio RIVO exceeds 40%, timerequired for retarding the phase for the desired angle by VYC 113becomes longer than the time required for varying the valve operationangle. Accordingly, the delay in reaching target closing timing IVCmight occur, and thus, the longer response time might be required.

Thus, in the combination of VEL 112 and VTC 113 of the presentembodiment, it is preferable to set ratio RIVO within the range from 0%to 40%, in order to shorten the response time required for varying theintake air amount and improve the response.

Regarding Fuel-Saving at Transient Operation

In investigating the fuel consumption at the transient operation,suppose that the vehicle is in an operation pattern shifting from theacceleration state by stepping on the accelerator pedal to theconstant-speed operation by decelerating by releasing the acceleratorpedal, namely, in the operation pattern opposite to that indicated inFIG. 21.

In this operation pattern, closing timing IVC of intake valve 105 isquickly advanced from an angle after the bottom dead center to an anglebefore the bottom dead center, so that the pumping loss can be reducedand thus the fuel consumption can be reduced. Moreover, by employing VEL112 configured to retard the center phase in response to the increase inthe valve operation angle, closing timing IVC can be quickly advanced,and accordingly, the reduction of the fuel consumption can be achieved.

FIGS. 25 and 26 show the change in valve operation angle operated by VEL112, the change in advance amount of phase operated by VTC 113, and thechange in opening timing IVO/closing timing IVC of intake valve 105,during deceleration. FIG. 25 shows the case where ratio RIVO is 50%, andFIG. 26 shows the case where ratio RIVO is 30%.

In the case where there is employed VEL 112 in which the center phasedoes not vary while the valve operation angle is varied, namely, ratioRIVO is set to be 50%, it is necessary to advance the phase for 32 degby VTC 113, as shown in FIG. 25(B). The time required for advancing thephase for 32 deg limits the time required for dosing timing IVC to reachthe target timing, and thus closing timing IVC takes 0.25 sec to beadvanced to the target timing.

In contrast, in the case where there is employed VEL 112 in which ratioRIVO is set to be 30%, since the center phase is advanced in response tothe decrease in the valve operation angle, VTC 113 is required toadvance the phase for only 8 deg (see FIG. 26(B)), and accordingly,closing timing IVC can be advanced to the target timing in 0.12 sec.

Thus, by employing VEL 112 that advances the center phase in response tothe decrease of the valve operation angle, the time required foradvancing closing timing IVC to the target timing can be reduced, andthus, the fuel consumption during deceleration can be reduced.

FIG. 27 shows a correlation between ratio RIVO and the fuel savingbenefit, and shows rapid decrease in the fuel saving benefit from thetime point where ratio RIVO exceeds 30%. Thus, it is preferable to setratio RIVO within the range from 0% to 30%.

In other words, when ratio RIVO exceeds 30%, the time required forperforming advance operation by VTC 113 exceeds the time required fordecreasing the valve operation angle, and thus, for this excess in time,the delay in advancing the closing timing IVC to the target timingoccurs.

On the other hand, when ratio RIVO is 30% or less, the time required forperforming advance operation by VTC 113 is less than the time requiredfor decreasing the valve operation angle, and thus, closing timing IVCcan be advanced to the target timing with good response, so that thepumping loss can be decreased quickly, and accordingly, the fuelconsumption can be reduced.

In the vertical axis of FIG. 27 representing the fuel saving benefit, asthe value gets greater, the fuel consumption becomes less.

Regarding Engine Stall Resistance

FIG. 28 shows the difference in opening timing of intake valve 105between the constant-speed operating state at the vehicle speed of 40km/h and an idle operating state, at engine cooling time.

During idle operation, in order to ensure the combustion stability, itis preferable to set opening timing IVO and closing timing IVC of intakevalve 105 in a manner that; the valve overlap amount is decreased toreduce the residual gas amount in a cylinder and introduce more freshair therein; and closing timing IVC of intake valve 105 is set at thevicinity of the top dead center, to thereby improve an effectivecompression ratio.

Thus, in the operation pattern shifting from the constant-speedoperation to the idle operation by releasing the accelerator pedal to befully closed, it is necessary to quickly retard opening timing IVO ofintake valve 105, to thereby quickly reduce the valve overlap amount, inorder to maintain the engine stall resistance.

However, in the case where VEL 112 that retards the center phase inresponse to the increase in the valve operation angle, the center phaseis advanced in response to the decrease in the valve operation angle.Thus, although opening timing IVO is required to be retard quickly, VEL112 is operated in the direction of advancing the opening timing IVO,and thus, this movement of VEL 112 hinders opening timing IVO from beingretarded.

FIGS. 29 and 30 show the change in valve operation angle operated by VEL112, the change in advance amount of phase operated by VTC 113, and thechange in opening timing IVO/closing timing IVC of intake valve 105, inthe operation pattern shifting from the constant-speed operation to theidle operation. FIG. 29 shows the case where ratio RIVO is 50%, and FIG.30 shows the case where ratio RIVO is 0%.

As shown in FIG. 29, in the case where there is employed VEL 112 inwhich both ratio RIVO and ratio RIVC are set to be 50% and the centerphase does not vary while the valve operation angle varies, openingtiming IVO can be retarded to the target timing by retarding the phasefor only 30 deg by VTC 113. In contrast, in the case where there isemployed VEL 112 in which ratio RIVO is set to be 0% so that openingtiming IVO does not vary while the valve operation angle varies and thevalve operation angle is decreased by advancing closing timing IVC, itis necessary to retard the phase for 40 deg by VTC 113.

Then, because of the difference in the required retard manipulatedvariable of the VTC 113, if ratio RIVO is 50%, opening timing IVO takes0.16 sec to reach the target timing, whereas if ratio RIVO is 0%,opening timing IVO takes 0.22 sec to reach the target timing. Thus, fromthe viewpoint of engine stall resistance, it is undesirable to set ratioRIVO to an extremely small value.

Here, it should be noted that the response time for varying openingtiming IVO can fall within the allowable range, if ratio RIVO is setwithin the range from 20% to 50%, as shown in FIG. 31.

As will be understood from the description above, as ratio RIVOapproaches 50% from 0%, the response and fuel consumption at thetransient operation become worse, on the other hand, as ratio RIVOapproaches 0%, the engine stall resistance gets worse.

Taking the above into consideration, it will be understood that, forsubstantially satisfying the response at the transient operation, thelow fuel consumption at the transient operation, and the engine stallresistance, ratio RIVO is to be set within the range from 20% to 40%,and more preferably, ratio RIVO is to be set at substantially 30%.

Therefore, in the present embodiment, by using VEL 112 in which ratioRIVO is set at 30%, the response at the transient operation, the lowfuel consumption at the transient operation, and the engine stallresistance can be wholly and successfully improved.

The entire contents of Japanese Patent Application No. 2008-136293,filed May 26, 2008 are incorporated herein by reference.

While only selected embodiments have been chosen to illustrate thepresent invention, it will be apparent to those skilled in the art fromthis disclosure that various change and modification can be made withoutdeparting from the scope of the invention as defined in the appendedclaims.

Furthermore, the foregoing description of the embodiments according tothe present invention is provided for illustrating purpose only, and notfor the purpose of limiting the invention defined by the appended claimsand its equivalents.

1. A controlling apparatus for an engine provided with: a variableoperation angle mechanism that is provided for varying a valve operationangle of an engine valve driven by a camshaft, and is capable of varyinga center phase of the valve operation angle in response to a variationin the valve operation angle; and a variable valve timing mechanismprovided for varying a rotating phase of the camshaft relative to acrankshaft of the engine, the apparatus comprising: a detecting unitthat detects an operating state of the engine; a first calculating unitthat calculates a target valve operation angle based on the operatingstate; a second calculating unit that calculates a target rotating phasebased on the operating state; a correcting unit that corrects the targetrotating phase based on the target valve operation angle; a firstoperating unit configured to calculate a first manipulated variable ofthe variable operation angle mechanism, based on the target valveoperation angle, to thereby output the first manipulated variable; and asecond operating unit configured to calculate a second manipulatedvariable of the variable valve timing mechanism, based on the targetrotating phase corrected by the correcting unit, to thereby output thesecond manipulated variable.
 2. The controlling apparatus according toclaim 1, wherein the engine valve comprises an intake valve, and whereinthe variable operation angle mechanism varies a center phase of a valveoperation angle of the intake valve in an advance direction in responseto a decrease in the valve operation angle.
 3. The controlling apparatusaccording to claim 2, wherein the variable operation angle mechanism isconfigured to operate under such a condition that a ratio of a changeamount of an opening timing of the intake valve to a change amount ofthe valve operation angle is set to be equal to or more than 20% andequal to or less than 40%.
 4. The controlling apparatus according toclaim 2, wherein the variable operation angle mechanism is configured tooperate under such a condition that a ratio of a change amount of anopening timing of the intake valve to a change amount of the valveoperation angle is set to be 30%.
 5. The controlling apparatus accordingto claim 1, wherein the second calculating unit calculates, when thevalve operation angle takes a reference value thereof, a rotating phasewhich brings the center phase of the valve operation angle of the enginevalve to be in coincidence with a target center phase which is setdepending on the operating state of the engine.
 6. The controllingapparatus according to claim 5, wherein the correcting unit comprises acorrection value calculating unit that calculates a correction valuebased on the target valve operation angle, and an add-subtract unit thatperforms addition of and subtraction between the target rotating phaseand the correction value.
 7. The controlling apparatus according toclaim 6, wherein the correcting value calculating unit calculates thecorrection value having a greater absolute value as the target valveoperation angle separates apart from the reference value.
 8. Thecontrolling apparatus according to claim 6, wherein the correction valuecalculating unit calculates a difference between a center phase of thevalve operation angle for when the valve operation angle takes thereference value thereof and the rotating phase takes a reference valuethereof, and a center phase of the valve operation angle for when therotating phase takes the reference value thereof and the valve operationangle takes a target value thereof, and then calculates the correctionvalue based on the difference.
 9. The controlling apparatus according toclaim 1, further comprising: a load detecting unit that detects avariation in an engine load; and a gain setting unit that sets a largergain in the first and second operating units, as the variation in theengine load turns abrupt.
 10. The controlling apparatus according toclaim 1, further comprising: a diagnosing unit that diagnoses whether ornot a failure of the variable operation angle mechanism occurs; and afailsafe unit that controls the variable valve timing mechanism so thatthe center phase of the valve operation angle of the engine valve isvaried in a direction separating apart from a top dead center of apiston, when it is determined that the failure of the variable operationangle mechanism occurs.
 11. The controlling apparatus according to claim10, wherein the failsafe unit controls the variable valve timingmechanism at a larger gain than that of when the variable operationangle mechanism is normal.
 12. The controlling apparatus according toclaim 10, wherein the engine valve comprises an intake valve, andwherein the failsafe unit is configured to set a target rotating phasein the variable valve timing mechanism to be a most retarded position,when the failure of the variable operation angle mechanism occurs.
 13. Acontrolling method of an engine provided with: a variable operationangle mechanism that is provided for varying a valve operation angle ofan engine valve driven by a camshaft, and is capable of varying a centerphase of the valve operation angle in response to a variation in thevalve operation angle; and a variable valve timing mechanism providedfor varying a rotating phase of the camshaft relative to a crankshaft ofthe engine, the method comprising the steps of: detecting an operatingstate of the engine; calculating a target valve operating angle based onthe operating state; calculating a target rotating phase based on theoperating state; correcting the target rotating phase based on thetarget valve operation angle: calculating a first manipulated variableof the variable operation angle mechanism based on the target valveoperation angle; outputting the first manipulated variable; calculatinga second manipulated variable of the variable valve timing mechanismbased on the corrected target rotating phase; and outputting the secondmanipulated variable.
 14. The controlling method according to claim 13,wherein the step of calculating the target rotating phase is executed toobtain a rotating phase which brings the center phase of the valveoperation angle of the engine valve to be in coincidence with a targetcenter phase which is set depending on the operating state of theengine.
 15. The controlling method according to claim 14, wherein thestep of correcting the target rotating phase comprises the steps of:calculating a correction value based on the target valve operationangle; and performing addition of and subtraction between the targetrotating phase and the correction value.
 16. The controlling methodaccording to claim 15, wherein the step of calculating the correctionvalue is executed to obtain the correction value having a greaterabsolute value as the target valve operation angle separates apart fromthe reference value.
 17. The controlling method according to claim 15,wherein the step of calculating the correction value comprises the stepsof: calculating a difference between a center phase of the valveoperation angle for when the valve operation angle takes the referencevalue thereof and the rotating phase takes a reference value thereof,and a center phase of the valve operation angle for when the rotatingphase takes the reference value thereof and the valve operation angletakes a target value thereof; and calculating the correction value basedon the difference.
 18. The controlling method according to claim 13,further comprising the steps of: detecting a variation in an engineload; and setting a larger gain for calculating the first and secondmanipulated variables as the variation in the engine load turns abrupt.19. The controlling method according to claim 13, further comprising thesteps of: diagnosing whether or not a failure of the variable operationangle mechanism occurs; and controlling the variable valve timingmechanism so that the center phase of the valve operation angle of theengine valve is varied in a direction separating apart from a top deadcenter of a piston, when it is determined that the failure of thevariable operation angle mechanism occurs.
 20. A controlling apparatusfor an engine provided with: a variable operation angle mechanism thatis provided for varying a valve operation angle of an engine valvedriven by a camshaft, and is capable of varying a center phase of thevalve operation angle in response to a variation in the valve operationangle; and a variable valve timing mechanism provided for varying arotating phase of the camshaft relative to a crankshaft of the engine,the apparatus comprising: detecting means for detecting an operatingstate of the engine; first calculating means for calculating a targetvalve operation angle based on the operating state; second calculatingmeans for calculating a target rotating phase based on the operatingstate; correcting means for correcting the target rotating phase basedon the target valve operation angle; first operating means forcalculating a first manipulated variable of the variable operation anglemechanism, based on the target valve operation angle, thereby outputtingthe first manipulated variable; and second operating means forcalculating a second manipulated variable of the variable valve timingmechanism, based on the target rotating phase corrected by thecorrecting means, thereby outputting the second manipulated variable.